Mozilla this week released Firefox 66, which by default now blocks all audio and video auto-play.

Other additions and enhancements to Firefox 66 included promised smoother scrolling, search within multiple tabs and clearer warnings of possible security problems on a website about to be rendered on the screen.

Engineers also patched 21 vulnerabilities, five of them labeled "Critical," Mozilla's highest threat ranking. "Some of these bugs showed evidence of memory corruption and we presume that with enough effort that some of these could be exploited to run arbitrary code," Mozilla reported.

Off with auto-play

The change to switch auto-play off by default was expected: More than a month ago, Mozilla announced that "with the release of Firefox 66 for desktop and Firefox for Android, Firefox will block audible audio and video by default."

To view video and listen to audio, users can click on the displayed play button, Mozilla said. They can also pull up site-specific controls which will allow some destinations to begin playing as soon as the browser pulls up a page. Muted auto-play video will also continue to be allowed; sound-free video is currently supported by all the major browsers that block auto-play media.

Mozilla

Firefox 66 users can set audio auto-play preferences on a per-site basis by clicking on the encircled "i" in the address bar.

Mozilla has been playing catch-up here to the likes of Google, which led in stymying audio auto-play. As long ago as 2013, Chrome blocked audio that blasted from opened tabs. Last year, it added stricter controls over auto-play, though it declined to block every site's audio.

Firefox 66 does much the same. "Subsequent videos will play automatically, just as the site intended ... ((on)) all streaming sites including Netflix, Hulu and YouTube," Nick Nguyen, Mozilla's vice president of product strategy, wrote in a March 19 post to a company blog.

Like many Firefox features, the auto-play blocking will be rolled out in stages, Mozilla said. Its plan: Offer it to 50% of users by March 21, all by March 26.

Unblocked for now: auto-play JavaScript Web Audio content, which is typically relegated to older web apps and online games. In early February, Mozilla said it was "working on blocking auto-play for Web Audio content" and was hoping to add blocking for that this year. Google added automatic blocking of auto-play Web Audio content in Chrome 66, but almost immediately backed off after users and developers complained that the change broke too many games and apps. Google restored the auto-play blockade with Chrome 71, which shipped in December 2018.

The staged roll-out was designed so that if Firefox 66 runs into the same kind of headwinds, Mozilla can quickly call a stop.

Streamline searches and security alerts

Firefox 66 added a search function to the tab overflow menu - that's under the downward-facing arrow at the far right when there are numerous open tabs - that automatically inserts a percentage sign (%) in the address/search bar. Any searches then show pertinent open tabs in the drop-down list.

Improvements were also made to the baked-in warnings that appear when the browser believes there's a problem with the site-to-be-seen's digital certificate. Legitimate certificates prove the site is what it claims it is. "If something isn't right, you'll get a security warning," Nguyen said. "We've updated these warnings to be simple and straightforward safe." Last week, Mozilla posted "Before" and "After" examples here.

The next upgrade, Firefox 67, should reach users on May 14, according to the browser's current release calendar.